Molding pattern



I May 30, 1944.. M. BEAN 2,349,806

MOLDING PATTERN 4 Filed Aug. 1, 1940 2 sheets-sheet 2 INVENTGR I PatentedMay 30,

MOLDING PATTERN Morris Bean, Yellow Springs, Ohio Application August 1', 1940, Serial No. 349,032

8 Claims.

i This invention relates to patterns for use in molding of plaster and the like. For a, long time, in the art of molding, the

advantages of using a flexible material for a pattern or mold have been recognized. Such iiexible material can be pulled away from undercut places without damage either to itself or the material molded against it, or to the material it is molded in, as the case may be. Hence, complex forms or shapes can be made from a single pattern or mold, where a complex pattern or mold of many parts would have to be used if it were made of a rigid material.

The advantages to be gained in the use of flexible patterns are of particular-interest for making molds bonded with plaster of Paris. It is a well known fact that mold materials containing a substantial proportion of plaster of Paris can be gauged with water and made to flow in around the pattern as a fluid plastic, which will subsequently "set within a short space of time to a rigid solid having high strength and resistance to disintegration from mechanical abrasion.

There are, however, some obvious disadvan-V tages connected with the use of exible patterns or molds in some applications. It is apparent that a material pliable enough to offer distinct advantages in molding is also pliable enough so that it may notA hold its shape within close limits of variation. In making a series of casts, the pattern or mold may not rest in exactly the same position twice, it may' warp as internal Vstrains tend to neutralize, or it may shrink on account of the volatilization of some of the ingredients. f. l

It is accordingly an object of my invention to overcome these disadvantages and to provide a pattern structure which is adapted to reproduce form and dimensions accurately in a large number of casts made upon it. Another object of the invention is to produce such a pattern which will be capable of long life and repeated re-use.

` .Other objects and advantages will be apparent to those skilled in the art from the following specification.

I have overcome the diiilculties set forth above by a number of expedients which advantageously are used together, but many of which may be used independently with improvement over patterns known prior to my invention. According to my invention, a pattern formedvof a flexible resilient material is permanently attached to a rigid support which is fitted to the back vof the pattern. The result of this i's a ilexible pattern held fl'rmly and accuratelyr against the rigid piece of material so that it always returns to the same shape. The necessary iiexibility .and resiliency is attained in the thickness of the material which is designed with this end in view, Whereas, if thematerial is not made too thick detween the back and the molding surface, the body of the pattern is held sufciently rigid so that it will remain accurate, even. in minute detail of its surface, when a soft or fluid mix of plaster or the like is poured over it and allowed to set.

I have found, however, with patterns of this kind, that, unless special precautions are taken,y

changes in size and changes in shape by warp-J ing, etc., and changesin degree of iiexibility may occur over a period of time due to loss of certain ingredients, particularly plasticizers, contained in the material of which the pattern is made. I have found that this loss is most serious when the pattern is backed with a rigid stonelike material such as plaster of Paris or cement; and I have found that this is due to the capillary action of the porous material used for the backing. Inasmuch as plaster, cast over the back of the pattern, makes an ideal backing material in other respects, this has proven to-be a serious disadvantage.

Il have now overcome this disadvantage by coating the back of the pattern with a material which is impervious to the plasticizer or other fugitive ingredients. For this purpose I have used, for example, various waxes, including for example, paraffin, various lacquers and resins. including for example, shellac, vitreous materials, such -for example as water glass, and thin sheet materials, particularly metal foils.

Finally, I have found that there is great difference in the ability of flexible resilient materials to withstand the various conditions to which they are subjected in use as patterns for molding plaster and the like; and I have found great advantage in the use of a particular material not heretofore used for this purpose, known make' duiiiiculty in strippingI thermo-plastic; and its contraction example, Duprene, "Thiokol," and various Y, polymerization products.

I have found in the production of patterns from this and other thermo-plastic materials that there is a relatively high contraction of the material after it is injected into the mold and while it is cooling, and that this tends to draw the material away from the surface which is to be reproduced by the pattern with .formation of objectionable irregularities on the pattern surface. This I have now been able to overcome by treating the respective surfaces of the mold so that the thermo-plastic material adheres more strongly to the surface which is to be reproduced than to theback of the mold in which it'is formed. Thus I`may coat the face of the mold to increase the adhesion, provided that it is not increased in such a way that the pattern cannot subsequently be removed from the mold; or, more advantageously, I mayl treat the bach of the mold so as to permit the material on contracting to draw readily away from the bach and thus to exert little or no retractile force on the surface which is to be molded. Advantageously, treat the surface which is to be reproduced by amaterial which facilitates removal but to which the thermo=plastic material adheres substantially.

When the face of the mold is made of a po-v rous material such as plaster composition, I have found it particularly advantageous to use Aim pregnation oi the mold face with a hard wax, such las montan wax, and advantageously a partially reiined montan wax, e. s., a mixture of 50% rened and 50% unreined, or the surface may be impr-ated with a solution of a, phenolic condensation resin or other suitable hard resin. The material chosen for this purpose is one which impregnates and flows easily at a temperature which does not dehydrate the plaster; advantageously, as in. Vthe oase of montan wax, it is one which deters dehydration of the plaster by the hot thermo-plastic molded upon it; it should be a material the excess of which can be easily wiped ofi the' surface of the plaster to leave a clean, smooth face; it should not soften at the temperature reached when the hot thermoplastic is molded on its surface; it should not adhere to the thermo-plastic so strongly as to on the molded on solididca tion and/or, cooling should be sumciently low so that it does leave voids.

For the back I have found moet suitable a e2.: :t metal foil to which the am may here but which fiexes easily away i the h of the mold, or I may dust the back of the mold with talc, or graphite, or may treat it with an insoluble soap or other material to which the thermo-plastic does not`readily adhere.

In makina" a Korogel pattern, the folios general procedure is to be followed:

The Korogel is heated to aY temperature suiiiciently high so that it becomes duid and is poured or otherwise injected into the mold cavity betweenthese treated surfaces and then allowed tocool.; During the cooling and solidiiication of the Korogel there is relatively large contraction, which due to the treatment of the mold surfaces is accommodated entirely at the back of the mold, since the Korogel material is held more strongly at the face than at the back: and as a consequence the.Korogel remains molded accurately to every fine detai1 of theface of the mold.

After the Korogel is solidified, the mold may be opened by removing the back, i. e., the part the back or the mold, this may be stripped ofi or left on the back of the pattern, and in the latter casewill serve as a barrier against fugitive ingredients which might oth be absorbed out of the Korogel or other thermo-plmtic composition into the plaster backing by capillary action.

If foil is not left on the back or has not been used during the molding operation it is desirable"h at this stage to apply a coating of some material which will serve as a. barrier against loss oi fugitive ingredients. For this purpose i have found a coatins of para. or other was to be suitable.

then apply anchor means, distributed over substantially the entire area. of the back. These are preferably metallic members which are heated so as to parti embed themselves in the thermo-plastic body but to leave parts protecting which are later emded in the material which forms the bach. For `iV p -f coils have proven to be best adapted, since the opte halves oi the t embed thelves completely in the theoplastic and the bacs material otively, sivins thus closely spaced ancho means with a minimum oi' labor in their application. if desired, the heating may be supplied uniformly throughout the coil by me: an electric resistance current through the entire coil after ithas been laid in position on the bach of the plastic pattern. In some cases I have found it ad= vantageoue toV apply the ancho means before 'applying the coatto seal fugitive ingredients.

removed from' the front part of the mold.

The resulting pattern with its rigid back is now in condition for use in molding plaster; and the like, especially with plasters which are in .subi

stantially duid condition so that they form easily about the surfaces of the exible pattern without imposing stresses which would tend to distort the pattern. have found that molded articles may be succively formed on a single pattern in large numbers and all will accurately repro.

duce the e.: :o: surface form and dimensions.

My invention is applicable as well to molds for making itives as to patterns for making neganve impressions for molding positives. The difierence is essentially one of design of the product anduse which does not fundamentally affect the voperation of this invention. I shall, therefore, use the word "pattern" to include both types without reference to the technical distinction between patterns and molds. It should be remembered, however, that a molding'technique is used in making these exible patterns. The mold used in making a pattern out of a thermoplastic material is not to be confused in this discussion with such exible molds herein referred ...we of the coil form loops which to as patterns or with molds-which may be -made from the pattern after it is finished.

Althoughin the accompanying drawings I have shown a preferred embodiment of my invention and have described the same and Various modifications thereof in this specification, it is to be understood that these are not intended to be either exhaustive or limiting of the invention, but on the contrary are chosen for the purposes of illustrating the invention in order that others skilled in the art may so fully understand the invention, its principles and the application thereof, that they may embody it and adapt it in numerous forms, each as may be best suited to the requirementsof its particular use.

Referring to these drawings:

Fig. l is a. perspective view of the pattern with its rigid back;

Fig. 2 is a cross section of the same, with a plaster body molded on the pattern;

Fig. 3 is a perspective view of the back of the v Aiiexible pattern still in place on the negative im# pression mold and with the anchoring coils affixed in the back of the pattern ready for appli-- cation of the hardenable backing material;

Fig. 4 is a view in cross section similar to Fig. 2 showing the negative impression mold in which the pattern is formed; and

Fig. 5 is a plan view showing a chain link fab? preferred case, is composed of Korogel, At I5, Il

have shown the wire coils, mentioned above, by which the pattern I4 is anchored vto the rigid backing Il, and at I6 between the backing I0 and the pattern Il is a layer of impervious material, advantageously paraffin wax.

The plaster body I8 is made by pouring the plaster over the pattern I4, as is well known in connection with ordinary plaster molding technic. When the plaster has set and the molding is. therefore, complete, the fiexible pattern I4 is readily stripped from the molded article by reason of its smooth surface and its resilient exibility,

whereas, it is held securely tothe rigid backing III by means of the anchoring coils i5; and, by reason of the distribution of these coils, the stripping of the flexible material from the mold takes place without any concentration of the stresses which might tear or permanently deform the flexible pattern.

In Figs. 3 and 4, I have shown the pattern and certain steps and apparatus used in 'its manufacture. Fig. 4 shows the mold in which the thermo-plastic is formed and given the desired pattern surface. In vthis I have used a negative impression mold 2li, which may be modeled or carved in plaster, clay, hard wax, wood or other suitable material, or may be shaped by molding directly onto a surface which is to be reproduced in the pattern, for example, a plaster cast of the original. larly if a porousmaterial such as plaster is used, is preferably impregnated with a high melting point wax, such as montan Wax, advantageously Aa. partially refined montan Wax, or a phenol-u 'Ihe surface of this mold. particu-- to the back.

adhesion at the pattern face sufficient to prevent Athe Korogel from drawing away from the pattern face while it is congealing and yet adapted readily to be freed from `the Korogel after it has congealed. v y l Other coatings or'lubricating materials can be used `on vthe face'of the 'pattern mold instead of the wax or varnish; for example, the molds may be dusted with graphite, talc or bronzing powder,

.but always 'the treatment of this mold face at 22 is to be so` related to the treatment of the face (at 23) of the back 24 as to have a substantially greater adhesion tothethermo-plastic molded i inthe cavity.

To this end. I preferably cover the back sur@ face (at 23) of the cavity, away from the molding face 22, with a" metal foil 23 which is free to pull away from the mold face ,proper and thus to ac.

commodate theentire shrinkage of the thermoplastic at thesurface thus covered with foil. Other coatingsthan foil may be used for this purpose also. For example, a heavy coating of lubri eating material such as graphite, talc or bronzing powder, may be used provided always that the adhesion at the molding face 22 is kept stronger than the adhesion at the face 23 where contraction is to be concentrated.

With the mold parts assembled, as shown in Fig. 4, the hot fluid thermo-plastic is poured or otherwise injected into the mold, preferably f under a substantial pressure, and is allowed to congeal and cool in the mold. After cooling the pattern is stripped from the mold andis then provided with the anchoring means in the manner illustrated in Fig. 3.

In Fig. 3, I have shown the completed flexibie portion cf the pattern with coils of wire I5 laid over its back and distributed over sub- -stantially the entire area of the back. These coils are then heatedfor example, by pressing with la hot plate, by passing a resistance electrical current through them or by means of a ne Bumsen flame or otherwise, until a part of each turn is embedded in the thermo-plastic may terial; but leaving a part of these turns projecting from the back, as shown for example in Fig. 3, and the turns spaced for a plaster key.

Either before or after the application of the coils I5 an impervious coating may be applied If the metal foil has been used in the mold it may be left in position, but may make difliculty in applying the coils i5 unless the surfaces of the coil are sumciently rough or sharp to puncture the foil or the foil is otherwise ruptured at the point where the coil contacts.

The pattern with these anchoring coils i5 and the impervious backing I6 is ready for appli cation of the rigid backing lll. This I do preferably by placing the 'pattern thus prepared face down in a suitable mold and casting a plaster mix onto its back, thus forming in situ the rigid backing by `which the flexible pattern is supported throughout its use. The plaster mix or other plastic used for this purpose should be sufllciently fluid to flow around the wires of the coils I5 orv other anchoring means or should be tamped lightly to force it around the anchoring formaldehyde condensation resin such as Bakelite varnish may be used satisfactorily, to give a mold means but at the same time to avoid distortion of the pattern.

when the backing has ses the pattern with its backing keyed thereto throughout` its area may be removed from the mold and is ready for an anchoring means suitable for use in vmy invention. vThis is a chain mail fabric, which can bepartiallyembedded in the thermo-plastic and thebacking in the same way as the wire coils already described. lIt, has the advantage that asaaeoc it can be cut tothe size and shape or the back l of the mold, laid `over it and heated to embed itself in the mold all with somewhat less labor thanwiththeooils.

In my copending applications, Serial Numbers 487.527 and 487,528, illed May 18, 1943, I have claimed thev inventions divided from this application including particularly the anchoring of the pattern to the rigid back by wire coils and the use of foil or other releasing agent to concentrate shrinkage of the pattern material at the back rather than at the molding face.

What I claim is:

l. A pattern. for molding plaster and the like which comprises a resiliently ilexible body of plasticized vinyl chloride gel having its face a negative of the surface which is to be molded thereby, a rigid back of porous substantially rigid material, a layer between said ilexible body and said back which is impervious to the plastiching constituent of said vinyl chloride gel; and anchor Ameans embedded partiallyl in said ilexible body and partially in said back and distributed over the area common to said flexible body and the back.

2. A pattern for molding plaster and the like which comprises a resiliently flexible body of plasticized vinyll chloride gel having its face a negative 'of the surface which is to be molded in the plaster, a rigid back of porous substantially rigid material, and a layer between said flexible ibl'e resilient pattern element of a composition includinga fugitive ingredient, a substantially rigid backing of a porous material, and an intermediate layer of material impervious to said fugitive ingredient.

5. A molding pattern which comprises a sul stantially rigid back of cementitious material, closely spaced anchor members rigidlyembedded in said back and projecting therefrom distributed over the area of the pattern back, and a body ot resiliently lilexible thermo-plastic material iltted to said back and embedding the projecting portions of said anchor members and having its surface away from said back shaped in the desired pattern which is to be reproduced by molding therewith.

G A molding-pattern which comprises a substantially rigid back, anchor members comprising spaced loops rigidly embedded in said back and projected therefrom, distributed over the area of the pattern back, and a body of resiliently exiblematerial tted to said back and embedding the projecting portions of said anchor members and having its surface away from said back shaped in the desired pattern which is' to be re produced by molding therewith.

7.. .A molding pattern which comprises a substantially rigid back, wire coils having the loops thereof spaced andV rigidly embedded in said back body and said .back which is impervious to the` plasticizing constituent of said vinyl chloride gel. 3. A pattern for molding plaster and the like which comprises aresiliently ilexible body of plasticized vinyl chloride gel having its face a negative of the surface which is to be molded in the plaster, a rigid back of cementitious material, and reticulate anchor means embedded partially in said flexible body and partially in said back and distributed over substantially the entire area common to said flexible body and the back.

4. A molding vpatter'r'r which comprisesv a .ilexand projecting therefrom distributed over the' area of the pattern back, and a body of resiliently dexible material tted to said back and embedding the projecting portions of said wire coils and having Iits surface away from said back shaped in the desired pattern which is .to be reproduced by molding therewith.

8. A molding pattern which comprises a back I of plaster of Paris, anchor means partly embedded' in said plaster back and projecting therefrom, a coating of wax on the surface of the back which carries said anchor means and adapted to seal said surface against; the capillary eiect of the plaster, a body of resiliently flexible vinyl chioride-tricresyl phosphate gel itted tosaid back, embedding the projecting portions of said anchor means and shaped to the desired pattern.

- MORRIS BEAN. 

